In a technical field of optical communication, an optical transmitter with a tunable wavelength function has been commercialized. For example, a 10 G tunable XFP (10-Gigabit Small Form Factor Pluggable) module with a tunable TOSA (Transmitter Optical Sub-Assembly) has been commercialized.
A semiconductor laser such as a tunable laser diode (LD) is used for the tunable TOSA as a light emitting element. In order to stabilize an emission wavelength, the semiconductor laser is controlled in drive conditions based on a temperature monitor of the semiconductor laser, or is temperature-constant-controlled by using a thermoelectric cooler (TEC).
A specification in power consumption of a TOSA is defined at about less than 3.5 watts (W) in a normal operational temperature range (illustratively, −5° C. to +70° C.)
Meanwhile, in recent years, for the purpose of a high-density packaging of an optical transmitter, there is a demand for expanding the operational temperature range (illustratively, −5° C. to +85° C.) of the TOSA while maintaining the power consumption.
Further, there is a demand for a tunable SFP+ module in power consumption being less than 1.5 W in the normal operational temperature range (illustratively, −5° C. to +70° C.).
In view of the above background, it is important to reduce power consumption of the tunable TOSA (in other words, a laser module or a laser apparatus).